This monograph is devoted to the basic aspects of the physics of highly ex- cited (Rydberg) states of atom's. After almost twenty years, this remains a hot topic of modern atomic physics. Such studies are important for many areas of physics and its applications including spectroscopy, astrophysics and radio astronomy, physics of electronic and atomic collisions, kinetics and di- agnostics of gases, and low- and high-temperature plasmas. Physical phenom-...